PHP parser: braces around variables

Question

I was wondering, how is the semantics of braces exactly defined inside PHP? For instance, suppose we have defined:

$a = \"foo\";

then what

Answer 1

The brackets delimit where the variable name ends; this example should speak for itself.

$a = "hi!"

echo "$afoo";  //$afoo is undefined

echo "${a}foo";  //hi!foo

echo "{$a}foo";  //hi!foo

Also, this should spit out a warning; you should use

${'a'}

Otherwise it will attempt to assume a is a constant.